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Sodium (Serum) Concentration

Published: August 9, 2026Updated: August 17, 2026

This test measures the amount of sodium, a key mineral electrolyte, in your blood serum. Sodium helps regulate fluid balance and nerve function.

Quick summary

["Your sodium level helps doctors check if you’re retaining or losing too much fluid or electrolytes."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
34966-2
Short code
OF .10% NaCl NFr RBC
Synonyms
OF .10% NaCl NFr RBC
Category
electrolyte
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
4.2
Ref high
5.9
Critical range
2 N/A – 7 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
85041
SNOMED
900000000000003001
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Is Done

Doctors may order a sodium test to diagnose conditions like dehydration, kidney problems, heart failure, or high blood pressure. It can also help monitor long-term health in people with chronic illnesses or those on certain medications that affect sodium levels.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for a few hours before your blood is drawn. Wear a loose shirt or sweater to make drawing blood easier.

What Happens During the Test

A healthcare provider will clean the area with an antiseptic and insert a small needle into a vein in your arm. A small amount of blood is collected into a tube. The process usually takes a few minutes, and you may feel a brief pinch.

What the Results Mean

Results are typically reported as a concentration in milliequivalents per liter (mEq/L). While reference ranges vary by lab, very high or very low sodium levels can signal serious health concerns that require medical attention.

Reference range

Adult males: 4.2-5.9; Females: 3.8-5.1 x 10^12/LN/A

Specimen: serum

No special preparation required. Stay well hydrated.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Sodium Level

Frequently asked questions

How long does it take to get my sodium test results?
Results are usually available within 1–3 business days, depending on your lab and healthcare provider. Some labs may provide preliminary results sooner, but final reports are typically reviewed by a doctor.
Can I eat or drink anything before my sodium test?
You may drink water but avoid eating solid foods for 4–8 hours before your blood draw, unless your doctor specifies otherwise. Fasting helps ensure accurate results.
Will I feel any pain or discomfort during the blood draw?
Most people experience only a brief pinch or mild discomfort during the needle insertion. Some may feel a slight sting, but the procedure is quick and rarely causes lasting pain.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy